The present work focusses on machine learning assisted predictions of the fatigue crack growth rate (FCGR) of Ti6Al4V (Ti64) processed through laser powder bed fusion (L-PBF) and post processing. ...Various machine learning techniques have provided a flexible approach for explaining the complex mathematical interrelationship among processing-structure-property of the materials. In the present work, four machine learning (ML) algorithms, such as K- Nearest Neighbor (KNN), Decision Trees (DT), Random Forests (RF), and Extreme Gradient Boosting (XGB) algorithms are implemented to analyze the Fatigue Crack growth rate (FCGR) of Ti64 alloy. After tuning the hyper parameters for these algorithms, the trained models were found to estimate the unseen data as equally well as the trained data. The four tested ML models are compared with each other over the training as well as testing phase, based on their mean squared error and R2 scores. Extreme Gradient Boosting has performed better for the FCGR predictions providing least mean squared errors and higher R2 scores compared to other models.
Present work investigates the adequacy of stir casting technique using mixed salt route method to fabricate in situ Al-4.5Cu-6wt%TiB2 composites and further the variation of porosity present in cast ...composite with varying pouring temperature, pouring time and different types of gating systems. The casting was found to be effective and economical for top gating system amongst rest of the gating design. The microstructural analysis of cast composite was carried out to determine the physical morphology and distribution of the TiB2 and Al2Cu phases in the matrix with the help of scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis of cast composite shows the formation of TiB2 particles in the absence of intermetallic, hard and brittle compound Al3Ti. Microstructural characterization was tandem with optical and high-resolution transmission electron microscopy (HR-TEM) results. These castings were checked for surface defects or sub-surface cracks using dye penetrant and ultrasound test. The amount of porosities present in all the castings was then determine precisely using Archimedes’ Principle of buoyancy. The experimental results thus found were validated with the simulation results obtained by AutoCAST simulation tool and improvements were incorporated by optimization of gating systems using modelling and simulation technique.
The critical study is focused on improving ductility by maintaining higher strength of swaged Zircaloy-4 through specifically optimized annealing treatment. It has led to evolution of texture to ...obtain stable (21¯1¯0) pyramidal type in the microstructure, enhanced elongation up to ∼20%. An excellent combination of ductility and strength was achieved through low-strain-swaging followed by annealing optimization, unlike other resource-intensive and conventional SPD techniques. Improvements in mechanical properties, especially ductility enhancement, were substantiated with the detailed and targeted microstructural analysis with EBSD and TEM.
In the present study, the fatigue crack propagation in 5052 Al alloy processed through different cryogenic rolling methods has been investigated in detail. The solution-treated 5052 Al alloy was ...subjected to different cryogenic rolling methods such as cryorolling (CR), cryo groove rolling (CGR) and cryo groove rolling followed by warm rolling (CGW). The CR, CGR and CGW processed samples exhibit threshold stress intensity value (Δ
K
th
) of 4.88, 6.5 and 5.5 MPa m
1/2
, whereas ST sample possesses Δ
K
th
of 3.75 MPa m
1/2
. The formation of UFG grains of size 125–200 nm as observed through the TEM images along with improved elastic strength of the cryo deformed samples are responsible for the improvement of Δ
K
th
.
Abstract
The compressive properties and 3 body wear characteristics of powder metallurgical (PM) processed Al/Si
3
N
4
/Al
2
O
3
P
Nanocomposites with single and combined reinforcement of Al
2
O
3
...and Si
3
N
4
reinforcing particles having different compositions (1%, 2% and 3%) were studied and evolution of microstructure, grain boundary character and micro texture of fabricated Al/Si
3
N
4
/Al
2
O
3
P
Nanocomposites was investigated through EBSD in the present research work. The fraction of high angle boundaries (HAGBs) were observed more in combined reinforcing samples of Al
2
O
3
and Si
3
N
4
whereas a single reinforcing sample of Al
2
O
3
and Si
3
N
4
showed fewer HAGBs. Micro texture results showed the strong textures components near to {112}〈111 〉 Cu and {110}〈111 for pure sintered Al sample P and mixed reinforcement composites (M
1
, M
2
and M
3
) > P whereas for single reinforcing sample showed weak textures near to transverse direction. Out of all fabricated composites, 2% mixed Al
2
O
3
and Si
3
N
4
reinforced composite revealed the maximum ultimate compressive strength (209.98 MPa) and least wear rate (0.1 mm
3
/min mm
3
/N-cm for 1 kg load and 3.5 mm
3
/N-cm for 2 kg load) attributing formation of nanocluster causing grain boundary pinning effect. The dominant failure mechanism for all samples was also detected and found to be a mixed-mode ductile failure mechanism for 2% mixed Al
2
O
3
and Si
3
N
4
reinforcement composite while other sample failed through ductile as well as mixed-mode mechanisms.
This study aims to numerically validate and simulate the fatigue crack growth rate (FCGR), tensile, and fracture toughness properties of T3 and T351 tempered aerospace grade Al 2024 alloy. The ...extended finite element method (XFEM) coupled with a genetic algorithm (GA) was used to predict FCGR behavior in the framework of an in‐house developed MATLAB code. The numerical simulation was performed using three different FCGR models, i.e., Paris, Forman, and Nasgro. The FCGR prediction ability of simulation models was improved and compared further using GA. The Nasgro model with genetically optimized parameters shows the highest FCGR prediction accuracy compared to other FCGR models. The critical stress intensity factor and von Mises stress distribution under static loading were also predicted for C(T) specimen. A similar XFEM approach was used for analyzing the tensile behavior using a center cracked specimen at the gage section of a dog bone‐shaped specimen.
Highlights
XFEM‐based MATLAB codes have been developed to analyze FCGR of Aluminum 2024 alloy.
Material constant was optimized using genetic algorithm to improve prediction accuracy.
The XFEM model could predict FCGR in differently cracked samples.
The XFEM model is used to predict the tensile and fracture behavior of Al alloy.
•MATLAB based XFEM codes has been developed to analyze FCGR of Additively manufactured Ti alloy.•The XFEM model could predict FCGR in differently cracked samples under mode I and mixed-mode ...loading.•The modified XFEM implemented through Abaqus model could elucidate the fracture toughness of Ti alloy.•The XFEM model is used to predict the tensile and fracture behavior of Ti alloy.
The mechanical properties such as tensile, fracture toughness, and fatigue properties of Additive Manufacturing (AM) fabricated Ti6Al4V alloy is critically crucial for structural applications. The in-house developed MATLAB-based extended finite elements method (XFEM) model has been utilized to analyse experimental results of fatigue, fracture, and tensile properties of AM fabricated Ti6Al4V alloy, to avoid expensive and destructive mechanical characterisation. The XFEM model was first used to validate the single edge cracked sample of laser powder bed fusion (LPBF) processed Ti6Al4V alloy for fatigue crack growth rate (FCGR). The XFEM simulation study was further extended to analyse fatigue life of center and double-side cracked specimens, as well as for evaluating fracture toughness KIC upon accounting potential crack initiation site. The model has also been developed to predict FCGR of edge cracked specimen under mixed-mode loading conditions. The critical stress intensity factor (SIF) and stress distribution map in the crack vicinity of the C(T) specimen were modelled through FEA Abaqus package to estimate the fracture toughness of Ti alloy. A similar XFEM approach was used to analyse the tensile properties of Ti alloy to predict its fracture behaviour through the center cracked specimen taken at the tensile gauge section. The strengthening mechanisms contributing to Ti alloy's static and dynamic properties are elucidated through microstructural characteristics of LPBF processed Ti6Al4V alloy reported in the literature.
Zirconium alloy demonstrates a favourable combination of strength, ductility, low neutron absorption cross-section, as well as excellent corrosion and oxidation resistance. In the context of its ...application as a reactor component, the critical hot deformation behaviour of isothermally swaged Zr-4 alloy has been extensively studied. Different combinations of elevated temperatures (873 K to 1023 K) and strain rates (0.01 s−1 to 10/s) have shown enhancement in flow stress. Analysis of stress flow, microstructural changes, and activation energy behaviour was performed using a state-of-the-art thermomechanical simulator with 50% reduction in sample thickness. The modified Arrhenius equation was employed to correlate theoretical and experimental flow stress behaviour. EBSD was utilized to understand texture evolution in hot deformed samples, revealing a transformation from pure basal to basal plus pyramidal poles concerning the compression direction. Texture evolution played a significant role in microstructural development, further characterized through TEM, which showed influential characteristics like subgrain boundaries, dislocations, and precipitate behaviour. Dynamic recrystallization mechanisms in swaged Zr-4 hot deformed samples were analysed using bright and dark field TEM modes, which were subsequently correlated with other microstructural characteristics such as grain morphology and structural defects.
•DRX is the dominant mechanism at the lower strain rate of 0.01 s−1 at 873 K and 923 K and for 0.1 s−1 strain rate at 923 K.•The texture evolution has transformed from basal to basal plus pyramidal poles in normal to compression direction.•Grain refinement and higher dislocation density has been observed at 923 K and 1 s−1 strain rate.•The subgrain boundaries provides the nucleation points for the dynamic recrystallization grains and promote the progress of dynamic recrystallization.
The deformation behaviour of Al 2014 alloy under high strain rate dynamic load experienced in the actual service condition of aero-structural components is scarce in the literature. Therefore, Split ...Hopkinson Pressure Bar (SHPB) based high strain rate compressive behaviour (dynamic loading) of Al 2014 is investigated in this work. The wrought (WAR) form of Al 2014 alloy has been chosen to examine its deformation behaviour with varying high strain rate compressive loading, generated through 4 different pressure ranges (1 bar, 1.5 bar, 1.75 bar, and 2 bar) at striker bar end in SHPB technique. These pressure ranges induced high strain rates 5536/s, 6236/s, 6576/s, and 7783/s in separate WAR specimen, correspondingly, which were recorded as flow stress curves. Also, the WAR Al 2014 alloy was heat treated with standard Tempered-6 (T6) condition to homogenize its microstructure. The T6 condition was exposed further with the same pressure values, which induced high strain rates 5303/s, 6139/s, 6977/s, and 7861/s in T6 specimens. The SHPB-based flow stress responses for both WAR and T6 conditions were compared to understand high strain rate deformation behaviours. The WAR specimen exposed at 7783/s strain rate has shown superior Peak Stress (P.S., ∼765 MPa) and %contractionP.S. (∼15%) compared to its T6 counterpart (at 7861/s). Prior to the dynamic studies, the quasi-static responses were also explored through tensile, compressive and hardness measurements (with WAR and T6) to realize the overall materials' behaviour. These dynamic responses under high strain rate compressive loading were correlated with in-process microstructural evolution, explored through SEM and XRD techniques. Exhaustive EBSD analysis quantified the excellent peak stress and % contraction in WAR conditions due to presence of huge amount of low angle grain boundaries (∼85%), ultrafine grains, relatively textured microstructure ({111} 〈100〉, {101} 〈001〉, etc), and significant strain hardening phenomena, whereas large amount of high angle grain boundary (∼88%), equiaxed and uniform microstructure contributed for higher hardness (∼22%) and tensile strength (∼2%) in T6 conditions.
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•Studied impact dynamic behaviour of Al2014 alloy using Split Hopkinson Pressure Bar (SHPB) method.•The peak stress and %−contractionP.S. in WAR impacted specimens were significantly higher than T6 impacted specimens.•The influence of crack morphology, with respect to strain rate, on mechanical properties are explored in detail.•EBSD analysis has been utilized exclusively to understand SHPB effect on microstructure-property correlation.•SEM micrography has revealed the SHPB strain rate effect on microstructural evolution, and tension-compression properties.
The objective of this study is to understand the suitability of mixed salt route using stir casting technique to fabricate in-situ Al-4.5%Cu-xTiB2 (x = 3, 6, 9 and 12 wt %) composites. The mechanism ...behind titanium/boron-based phase evolution in Al-Cu alloy has been enlightened first time, particularly its strong influence over mechanical behaviour was examined. The in-situ TiB2 reinforcement particles were prepared by the exothermic reaction of K2TiF6 and KBF4 salts in melted aluminium copper alloy which improves the hardness, yield, and tensile strengths to the extent of ∼89 VHN, ∼236 MPa and ∼295 MPa, respectively. Preliminary microstructural evolution was analysed and discussed through optical microstructures and proposed mechanism. The composites were characterized carefully with the help of field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) to know the morphological details and TiB2 distribution in the aluminium matrix composite (AMC) microstructure. In support with electron microscopic observations, the X-ray diffraction (XRD) and Electron Probe Microscopic Analysis (EPMA) were also performed. To further enhance the mechanical properties, T6 heat treatment (HT) was done. During the HT process, the composites were solutionized at 540 °C for two hours followed by water quenching. After that, artificial ageing was carried out at 170 °C with varying durations of 5, 10, 15, 20, and 25 h and post-ageing effect on the mechanical properties were recorded. Composites were thermally characterized through differential scanning calorimetry (DSC) to learn the precipitation kinetics and compared with alloy chosen.
•Thermodynamics of TiB2 precipitation explained through Miedema model.•HR-TEM discerned the associated detailing of particle/matrix interface.•Intermetallic phases investigated through Electron Probe Micro Analysis.•Mechanism of TiB2 evolution and its correlation with tensile and hardness properties.
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